There are prior art conventional presses having a ram with a top tool which is pressed with great force against a workpiece on a bottom tool on a press table by one or more hydraulic cylinders. The workpiece is hereby retained between the tool parts with a blankholder force.
A punch connected to the frame of the press is forced through coaxial openings in the tool parts whereby an workpiece is shaped. The punch is retracted to a position outside the workpiece. Hereby, the workpiece will project into the opening of one of the tools.
The finished workpiece is ejected by lifting the top tool to a position where it is possible to remove the finished workpiece from the press. Particularly by deep workpieces, this is a drawback as the top tool has to be moved a relatively great distance before the workpiece may be ejected.
The distance by which the top tool is to be lifted greatly influences the cycle time and the energy consumption of the press.
In JP 03 295 004 B2 is indicated a press with a lower and an upper press bed. The upper press bed is provided with an upper tool and the lower press bed is provided with a lower tool. The two tools are provided opposite each other while the workpiece is pressed. The workpiece is shaped in that a punch connected to a cylinder which is connected to the frame of the press is pressed against the workpiece and draws it into an opening in the upper tool.
When the workpiece is to be ejected, the upper press bed is moved from a pressing position to an ejecting position. The upper press bed is displaced horizontally between the two positions.
A device for introducing workpieces and a device for ejecting the finished workpiece are directly connected to the upper press bed. When a workpiece is to be ejected, the upper press bed is moved to the ejection position at which the workpiece is ejected. At the same time, the device for introducing workpieces is moved to a position above the lower tool. The workpiece is placed on the tool and the upper press bed is moved to a pressing position. The device for introducing workpieces receives a new workpiece while the already introduced workpiece is pressed.
The upper press bed is connected to the machine frame through a rail arrangement. The frame is open at the top such that the devices for ejecting the workpiece and introducing a workpiece, respectively, can be displaced horizontally without colliding with any part of the machine.
A drawback of the press indicated in JP 03 295 004 B2 is the relatively large mass to be moved each time a workpiece is to the ejected and a new workpiece introduced.
The mass of the upper press bed, the upper tool, the device for ejecting the workpiece and the device for introducing workpieces are to be accelerated in speed for moving to the ejection position, braked for ejection, accelerated in opposite direction for moving to the pressing position and braked for pressing. A press bed with relatively great speed requires relatively strong displacement means in order to attain a short cycle time. Alternatively, the cycle time becomes long.
The energy consumption of such a machine is relatively big if a short cycle time is desired.
Another drawback is the limit to the size of the area of the cut out in the upper press bed for the workpieces which may be shaped in the press, without the upper press bed having to be substituted by a second upper press bed with another dimension of the opening as the workpiece penetrates into the opening in the upper press bed.